JP2001098101A - Polyethylene-based crosslinked foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyethylene-based crosslinked foam, having excellent characteristics of polyethylene-based crosslinked foam, and also excellent in resistance to heat, formability or the like. SOLUTION: This polyethylene-based crosslinked foam has a heat of fusion of 60 to 160 J/g, determined by differential scanning calorimetry effected at 110 deg.C or higher. It is preferably produced by crosslinking foaming of a polyethylene-based resin containing a low-density polyethylene produced by the high pressure method at 20 wt.% or more and straight-chain, low- to medium-density polyethylene having a density of 0.94 g/cm3 or less at 10 wt.% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a crosslinked polyethylene foam. For more details, cushioning materials for automobile interiors,
Properties related to polyethylene-based cross-linked foams that have properties that can be applied to various types of molding methods under heating applicable to insulation materials for building materials, industrial materials, furniture, household appliances, etc., and are particularly excellent in moldability and heat resistance It is.

[0002]

2. Description of the Related Art Polyethylene foams are excellent in lightness, heat insulation and sound insulation, and are processed into various shapes by slitting or punching, and are used for building materials formed by bonding to packings, bath mats, and iron plates. It is widely used in the fields of heat-insulating folded-plate roofing materials and cushioning materials for automobile interiors due to its excellent heat moldability.

[0003] Many technologies relating to polyethylene foams have already been introduced. Polyethylene foams include non-crosslinked foams formed by extrusion foaming and crosslinked foams in which a resin component has a crosslinked structure introduced by electron beam crosslinking, peroxide crosslinking or silane crosslinking. In particular, crosslinked foams are often used for applications requiring
As a method for producing a polyethylene-based crosslinked foam, after kneading a decomposable foaming agent into polyethylene and forming it into a sheet,
Ionizing radiation, generally irradiating with an electron beam to crosslink,
After foaming by heating at or above the decomposition temperature of the foaming agent, or peroxide and a peroxide are mixed at the same time, kneading at a temperature at which the peroxide and the foaming agent do not decompose similarly, and after forming into a sheet, In general, a method of crosslinking by heating to a temperature at which the peroxide decomposes and foaming by heating is used.

On the other hand, linear low-density polyethylene obtained by copolymerizing ethylene with an α-olefin has been developed to improve the physical properties and productivity of high-pressure low-density polyethylene. For a cross-linked foam using a resin or a resin mixed with high-density low-density polyethylene, see JP-B-2-57577 and JP-A-2-57578.
It is introduced by the official gazette.

[0005]

A crosslinked foam made of high-pressure low-density polyethylene is inferior in mechanical properties such as tensile strength. Crosslinked foams composed of high-pressure low-density polyethylene and linear low-density polyethylene obtained by copolymerizing ethylene with an α-olefin have excellent tensile strength and heat moldability, but have heat resistance depending on applications such as automotive interior applications. In some cases, there is a shortage, and improvement has been strongly desired.

[0006]

Means for Solving the Problems The present inventors have studied in detail a polyethylene-based crosslinked foam having particularly excellent properties of heat resistance and moldability. As a result, the heat of fusion of 110 ° C. or more by differential scanning calorimetry was found. The polyethylene-based crosslinked foam of 60 to 160 J / g has particularly high heat resistance in addition to the excellent properties of the conventional polyethylene-based crosslinked foam such as moldability, flexibility and cushioning property, and is used for automotive interior materials or heat insulation. The present invention was found to be suitable for a pipe cover or the like as a material, and led to the present invention.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The “heat of fusion of 110 ° C. or more by differential scanning calorimetry” of a foam according to the present invention is defined by JI
Among the heat per unit weight obtained from the melting peak area of the differential scanning calorimetry by the differential scanning calorimeter (DSC) measured in accordance with SK-7122-1987, the heat of fusion of 110 ° C. or more, Hereafter, this 110
The heat of fusion at or above ° C is denoted as ΔHm (110 ° C). In the present invention, "high heat resistance" means, for example, 110
The dimensional change of the foam under heating near the melting point of polyethylene, such as ℃, is small, or the cells of the foam are destroyed under heating and pressurization or local cells during the secondary processing under heat molding such as vacuum molding of automobile interior materials. This means that blisters and the like due to expansion are unlikely to occur.

In the present invention, ΔHm (110 ° C.) is 60
To 160 J / g. Particularly, as a foam for an automobile interior requiring high flexibility, cushioning property and heat resistance, 70 is used.
It is preferable that it is 140 J / g. ΔHm (110
C.) is less than 60 J / g, sufficient heat resistance may not be obtained. When ΔHm (110 ° C.) is 160 J / g or more, the buffering property may be poor, and it may be unsuitable especially for automotive interior materials.

The resin component of the foam according to the present invention contains a polyethylene resin as a main component. As the polyethylene resin, high-pressure low-density polyethylene, α-
Olefin copolymerized linear low-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-propylene copolymer, ethylene- (meth) alkyl acrylate copolymer, Examples include ethylene-propylene-diene rubber (EPDM), a terpolymer obtained by copolymerizing maleic anhydride as a third component with a copolymer of ethylene and a mixture thereof, and the like.

The polyethylene resin used in the polyethylene foam of the present invention includes a high-pressure low-density polyethylene (A) in order to impart good productivity and appearance, physical properties such as tensile strength and elongation, and heat moldability. ) And linear low / medium density polyethylene (B) having a density of 0.94 g / cm ³ or less are preferably contained as components thereof.
It is more preferable that (A) is contained in an amount of 20% by weight or more and (B) is contained in an amount of 10% by weight or more, and it is more preferable that (A) is contained in an amount of 20% by weight or more and (B) is contained in an amount of 30% by weight or more.

The above high-pressure low-density polyethylene resin (A)
The method is not particularly limited to a production method, but is generally a polymerization by a high-pressure radical polymerization method represented by a tubular type or an autoclave type reactor, and among them, an autoclave type reactor is preferable. In the present invention, two or more high-pressure low-density polyethylene resins can be used in combination as (A). The density is preferably 0.915 to 0.937 g / cm ³ ,
More preferably, it is 0.925 to 0.937 g / cm ³ . If the density is less than 0.915 g / cm ³ , sufficient heat resistance may not be obtained. In addition, the density is 0.937
If it exceeds g / cm ³ , the crosslinkability may be extremely deteriorated. The MFR is preferably from 1 to 10 g / 10 minutes, more preferably from 2 to 8 g / 10 minutes. If the MFR is less than 1 g / 10 minutes, the foaming agent may be decomposed due to shearing heat during extrusion and a good foaming sheet may not be obtained. On the other hand, if the MFR exceeds 10 g / 10 minutes, it is preferable in terms of extrudability. However, mechanical properties such as tensile strength and elongation may decrease.

The linear low- / medium-density polyethylene resin (B) used in the present invention includes ethylene and carbon atoms having 4 to 12 carbon atoms.
Is a linear low-density or medium-density polyethylene resin copolymerized with an α-olefin. The resin (B) can be produced by a gas phase method using a Ziegler type catalyst, a solution method,
A slurry method is generally used, and the type of α-olefin copolymerized with ethylene is not particularly limited, but a binary copolymer of ethylene and α-olefin is generally preferable. -The olefin having 4 to 8 carbon atoms is advantageous from the viewpoint of both price and physical properties, and is preferred. Further, in the present invention, two or more kinds of linear low / medium density polyethylene resins can be used in combination as (B). Its density is at 0.94 g / cm ³ or less, preferably 0.92~0.94g / cm ^3. When the density is less than 0.92 g / cm ³ , the flexibility of the resin is remarkable, stickiness is caused, and when the foam is used, blocking is apt to occur, and the mechanical strength and the stiffness of the foam are reduced, and the heat resistance is also low. May be. On the other hand, if the density exceeds 0.94 g / cm ³ , the foam may be hard and the cushioning property may be deteriorated. The MFR is preferably 0.7 to 20 g / 10 min, more preferably 1 to 20 g / 10 min.
15 g / 10 min, more preferably 2 to 8 g / 10 min.
Minutes. If the MFR is too high, mechanical properties such as tensile strength and elongation decrease, while if it is too low, the foaming agent is decomposed due to heat generated by shearing during extrusion, and a good foaming sheet may not be obtained.

When the high-density low-density polyethylene (A) is less than 20% by weight, the melt tension is too low, so that even if cross-linking, gas is easily released and a good foam is hardly obtained, and cross-linking may be difficult. . If the linear low / medium density polyethylene (B) is less than 10% by weight, tensile elongation and strength may be insufficient.

In the present invention, ΔHm (110
(C) satisfying 60 to 160 J / g, it is preferable to add a high-density polyethylene resin (C) in addition to the above components (A) and (B) as necessary. Here, the high-density polyethylene resin (C) has a density of 0.94 g / c.
m very small amount of carbon atoms and ³ or more polyethylene or ethylene is polyethylene resin obtained by copolymerizing 4-12 α- olefins. As the high-density polyethylene, those having a straight chain or those having a long chain branch are known, and both are suitably used. Its density is 0.94 g / cm ³ or more, preferably 0.945 g / cm ³ or more. The MFR is preferably 0.3 to 25 g / 1.
0 minutes, more preferably 1 to 15 g / 10 minutes, and still more preferably 2 to 8 g / 10 minutes. If the MFR is too high, mechanical properties such as tensile strength and elongation decrease, while if it is too low, the foaming agent is decomposed due to heat generated by shearing during extrusion, and a good foaming sheet may not be obtained.

In the present invention, a crosslinked structure is introduced into the foam.
As a method of producing a polyethylene-based crosslinked foam, a polyethylene raw material is kneaded with a decomposable foaming agent, formed into a sheet, and then irradiated with ionizing radiation, generally an electron beam, to be crosslinked. The foaming is performed by heating as described above, or the peroxide is mixed with the foaming agent and kneaded at a temperature at which the peroxide and the foaming agent are not decomposed. Cross-linking by heating to the temperature
A method of foaming by heating is general. Crosslinking aids can be used as needed, either by electron beam irradiation or by crosslinking in the case of peroxides.

The crosslinking assistant is not particularly limited,
Divinylbenzene, trimethylolpropane trimethacrylate, 1,6-hexanediol methacrylate,
1,9-nonanediol dimethacrylate, 1,10-
Decanediol dimethacrylate, triallylic acid triallyl ester, triallyl isocyanate, neopentyl glycol dimethacrylate, 1,2,4-benzenetricarboxylic acid triallyl ester, tricyclodecane dimethacrylate, polyethylene glycol diacrylate, and the like, These may be used in combination of two or more.

The crosslinked foam of the present invention has a degree of crosslinking of 15 to 50.
% Is preferable, and more preferably 20 to 40%. If the degree of cross-linking is less than 15%, the foaming gas has a low holding power during the production of the foam, so that the foaming gas may dissipate from the surface, failing to attain a predetermined expansion ratio, or causing deterioration of the surface morphology. On the other hand, if it exceeds 50%, the cross-linking becomes dense, which is preferable in terms of foaming property and surface smoothness. However, the cross-linking becomes too dense, the holding power of the foaming gas becomes excessive, and partial destruction of bubbles occurs. May be void.

The expansion ratio of the crosslinked foam of the present invention is 5 to 50.
Times, and more preferably 7 to 40 times. When the expansion ratio is less than 5 times, the resin portion in the volume is large, so that it is preferable in terms of mechanical strength, elongation, and moldability, but the cushioning property may be reduced. On the other hand, if it exceeds 50 times, flexibility increases and it is preferable in terms of buffering property, but since the resin portion in the volume decreases, mechanical strength, heat resistance, and moldability may decrease. The draw ratio (L / D) representing the moldability of the crosslinked foam of the present invention is preferably 0.4 or more, more preferably 0.5 or more. If the drawing ratio is less than 0.4, it may not be able to follow a complicated molded shape and may be broken.

The resin component of the present invention includes the above (A),
(B) A thermoplastic resin having a melting point of 170 ° C. or less other than the resin may be mixed in an amount of 30 parts by weight or less based on 100 parts by weight of the total of (A), (B) and (C). Specifically, homopolypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene rubber (EPM), ethylene-propylene rubber-diene rubber (EPDM), ethylene-vinyl acetate copolymer, ethylene -Acrylic acid copolymer, ethylene-
Polyolefins such as terpolymers obtained by copolymerizing (meth) alkyl acrylate copolymers or copolymers thereof with maleic anhydride as a third component, or styrene-butadiene-styrene block copolymers, styrene -Butadiene copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-ethylene block copolymer, ethylene-butadiene-ethylene block copolymer and hydrogenated resins thereof. However, the addition of a crystalline thermoplastic resin having a melting point of 120 ° C. or lower or an amorphous thermoplastic resin having a glass transition temperature of 120 ° C. or lower is preferred in terms of flexibility and buffering property when the mixing amount exceeds 30 parts by weight, Heat resistance may decrease.

In addition, if necessary, heat stabilizers, weathering agents,
Known additives such as a flame retardant, a flame retardant auxiliary, a dispersant, a pigment, a flow improver, a release agent, and a filler may be added. The decomposition type foaming agent which can be applied in the present invention includes organic and inorganic various types.
N. N'-dinitrosopentamethylenetetramine;
Inorganic systems such as P'-oxybenzenesulfonyl hydrazide include sodium carbonate, ammonium carbonate, ammonium bicarbonate, calcium azide and the like.

In the present invention, as a method of crosslinking the resin portion of the foam, a radiation crosslinking method of irradiating with ionizing radiation is preferable, but dicumyl peroxide, tertiary butyl perbenzoate, ditertiary butyl peroxide, etc. A chemical cross-linking method in which 0.5 to 5 parts by weight of the above peroxide compound is added to 100 parts by weight of the resin component and cross-linking is performed can also be used. A known method can be applied to the foaming method according to the present invention. Specifically, those which can be manufactured as a continuous sheet such as a vertical hot air foaming method, a horizontal hot air foaming method, and a horizontal chemical liquid bath foaming method are preferable.

[0022]

EXAMPLES Next, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited by these. The measuring method and evaluation criteria in the present invention are as follows.

1. Degree of Crosslinking The foam is shredded and 0.2 g is precisely weighed. This is 130
Immersed in tetralin at room temperature and heated with stirring for 3 hours to dissolve the dissolved part. The insoluble part was taken out and washed with acetone to remove tetralin. Moisture is removed with a dryer, and the mixture is naturally cooled to room temperature. The weight W1 (g) of this product is measured, and the degree of crosslinking is determined by the following equation. Degree of crosslinking = [(0.2−W1) /0.2] × 100
(%)

2. Foaming ratio 10 x 10 cm was cut out from the foam and the thickness t1 (c
m) and weight W2 (g) are measured, and the apparent density is calculated by the following equation. Apparent density = W2 / (10 × 10 × t1) (g / cm ³ ) The expansion ratio is obtained from the apparent density by the following equation. Expansion ratio = 1 / apparent density

3. Drawing ratio Heat the foam surface to 130 ° C with an infrared heater and mold it with a vacuum forming machine equipped with a cup-shaped forming mold with a depth (L) to a diameter (D), and the foam is torn. And the maximum L / D ratio formed in a cup shape is defined as the drawing ratio. The larger the drawing ratio, the better the vacuum formability. 4. Heat shrinkage rate Cut out a 15cm x 15cm square sample from the foam, write a 10cm long perpendicular marked line parallel to each side at the center, put this sample in 110 ° C hot air circulation oven and heat for 1 hour Then, take out and cool naturally to room temperature. The length of each marked line of this heat-treated sample was measured, and the average value was defined as La (cm), and the heat shrinkage was calculated according to the following equation. Heat shrinkage (%) = [(10−La) / 10] × 100
(%) 5. MFR Measured at a temperature of 190 according to JIS K-6760.
Measure in ° C.

6. The heat of fusion of the foam at 110 ° C. or higher The sheet obtained by defoaming the foam by passing it through a cold mixing roll with zero clearance,
The sample is cut as a sample for measurement, and is measured by a differential scanning calorimeter
The sample was packed in a predetermined sample pan for C). The heat of fusion is JI
It was measured according to SK-7122-1987. Using an RDC220 robot DSC device manufactured by Seiko Denshi Kogyo, the above sample was heated from 25 ° C to 200 ° C at a heating rate of 1
Perform differential scanning calorimetry at 0 ° C / min.
A C melting curve was obtained. Next, the amount of heat of fusion per unit weight ΔHm (unit: J / g) was obtained from the area surrounded by the DSC melting curve and the baseline by the analysis job program. The DSC melting curve obtained by the above-mentioned DSC measurement was copied onto a high-quality paper, a portion surrounded by the DSC melting curve and the base line was cut out, the weight was measured, and the weight was measured as W0 (g).
And Next, a portion at 110 ° C. or higher was cut out of a region surrounded by the DSC melting curve and the baseline, and its weight was measured. The weight was defined as W1 (g). The heat of fusion ΔHm at 110 ° C. or higher (110 ° C.) (J / g) was calculated by the following equation. ΔHm (110 ° C.) = ΔHm × W1 / W0

Hereinafter, embodiments of the present invention will be described based on examples. [Example 1] As (A), a high-pressure method low-density polyethylene (density 0.923 g / cm ³ , MFR 7.0 g / 10
Min) 35 parts by weight, as (B) a linear low-density polyethylene obtained by copolymerizing ethylene with butene (density 0.934 g /
cm ³ , MFR 3.0 g / 10 min) 45 parts by weight, (C)
As high density polyethylene (density 0.960g / c
m ³ , MFR 7.0 g / 10 min) 20 parts by weight, and 0.3 parts by weight of “Irganox 1010” as a heat stabilizer in 15 parts by weight
After sufficiently kneading with a mixing roll set at 0 ° C., 5.9 parts by weight of azodicarbonamide as a decomposable foaming agent was further added and kneaded to obtain a foaming composition. Table 1 shows the composition of the foam. This mixed raw material is heated to a temperature at which the foaming agent does not decompose, specifically, to a thickness of 1.
A 2 mm sheet was made. This sheet has a gel fraction of 2
An electron beam was irradiated at an accelerating voltage of 800 kV so that the concentration became 6 ± 2% by weight to give a crosslink. The sheet was heated and foamed in a foaming bath on a silicone chemical bath heated to 225 ° C. to obtain a foamed sheet having a closed cell structure with a thickness of 2.9 mm. The expansion ratio of this sheet was 14 times, and the gel fraction was 26% by weight. A heat of fusion of 110 ° C. or more of the foam;
Table 2 shows the heat shrinkage at ℃ and the draw ratio.

Example 2 A foamed sheet was prepared in the same manner as in Example 1, except that 0.8 parts by weight of tricyclodecanedimethacrylate was added to 100 parts by weight of the resin as a crosslinking aid, as shown in Table 1. Created. Table 2 shows various physical properties of the foam sheet. Example 3 As (A), a high-pressure method low-density polyethylene (density 0.932 g / cm ³ , MFR 6.0 g / 10
Min), (C) as high density polyethylene (density 0.96
4 g / cm ³ , MFR 5.0 g / 10 min), and a foamed sheet was prepared in the same manner as in Example 1. Table 2 shows various physical properties of the foam sheet.

Example 4 The same procedure as in Example 1 was carried out except that 1.0 part by weight of 1,9-nonanediol dimethacrylate was added to 100 parts by weight of the resin as a crosslinking aid in the amounts shown in Table 1. A foam sheet was made. Table 2 shows various physical properties of these foam sheets. Example 5 As (B), a linear low-density polyethylene obtained by copolymerizing ethylene with butene (density 0.922 g / cm
³ , MFR 4.0 g / 10 min), and a foamed sheet was prepared in the same manner as in Example 1 except that the compounding amounts shown in Table 1 were used. Table 2 shows various physical properties of these foam sheets. [Comparative Examples 1 to 3] Foamed sheets were prepared in the same manner as in Example 1 except that the conditions of the resin, the compounding amount, and the crosslinking aid shown in Table 1 were used. Table 2 shows various physical properties of these foam sheets.

In Table 2, the heat resistance is 110 ° C.1
Those having a heat shrinkage rate of 4% or less over time were accepted. Heat moldability is required for automotive interior material applications and the like, and the moldability was determined to be acceptable if the drawing ratio was 0.4 or more. As shown in Table 2, the foam of Comparative Example 1 was inferior in moldability, and the foam of Comparative Example 3 was inferior in heat resistance and moldability. The foam of Comparative Example 2 had poor appearance due to outgassing. On the other hand, Example 1
The foams of Nos. To 5 were excellent in both moldability and heat resistance.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

The polyethylene-based crosslinked foam according to the present invention has a heat of fusion at 110 ° C. or higher as determined by differential scanning calorimetry of 60 to 160 J / g, and has particularly high heat resistance. A crosslinked foam made of a polyethylene resin containing a low-density polyethylene and a linear low-medium density polyethylene having a density of 0.94 g / cm ³ or less is particularly excellent in moldability. As described above, according to the present invention, it is possible to obtain a polyethylene-based crosslinked foam having the excellent properties of a polyethylene-based crosslinked foam and also having excellent heat resistance, moldability, and the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a DSC melting curve by differential scanning calorimetry, in which a hatched portion is a region surrounded by a DSC melting curve and a base line, and the heat of fusion per unit weight is calculated from the area of this region. Calculate ΔHm (J / g).

FIG. 2 is a diagram showing the same DSC melting curve as FIG. 1, wherein a hatched portion is a portion at 110 ° C. or higher in a region surrounded by the DSC melting curve and a baseline;
From the area of this region, the heat of fusion ΔHm (1
10 ° C.) (J / g) is calculated.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4F070 AA13 AB14 AB21 GA04 GC02 4F074 AA18 AA20 AA21 AB02 BA13 BB25 BB28 CA29 CC04Y CC06X CC45 DA02 DA04 DA22 DA23 DA24 DA32 DA33 DA37 DA47 4J002 BB03W BB05X DE226 DF006 EK006 EK016 EK016 FD147 FD150 FD326 GC00 GL00 GN00

Claims (5)

[Claims] 1. A crosslinked polyethylene foam having a heat of fusion at 110 ° C. or higher as determined by differential scanning calorimetry of 60 to 160 J / g. 2. A high-pressure low-density polyethylene having a density of 0.
94 g / cm ³ polyethylene crosslinked foam of the following claims 1, wherein the polyethylene resin is crosslinked foam containing a linear low and medium density polyethylene, characterized by comprising. 3. A polyethylene resin containing at least 20% by weight of high-pressure low-density polyethylene and at least 10% by weight of linear low- and medium-density polyethylene having a density of 0.94 g / cm ³ or less is cross-linked and foamed. The polyethylene-based crosslinked foam according to claim 1 or 2, wherein: 4. The crosslinked polyethylene foam according to claim 1, wherein the degree of crosslinking is 15 to 50% and / or the expansion ratio is 5 to 50 times. . 5. The polyethylene-based crosslinked foam according to claim 1, wherein the draw ratio is 0.4 or more.